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61A Lecture 2
Announcements
Names, Assignment, and User-Defined Functions
(Demo)
Types of Expressions
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Types of Expressions
Primitive expressions:
4
Types of Expressions
Primitive expressions: 2
Number or Numeral
4
Types of Expressions
Primitive expressions: 2 add
Number or Numeral Name
4
Types of Expressions
Primitive expressions: 2 add 'hello'
Number or Numeral Name String
4
Types of Expressions
Primitive expressions:
Call expressions:
2 add 'hello'
Number or Numeral Name String
4
Types of Expressions
Primitive expressions:
Call expressions:
2 add 'hello'
max ( 2 , 3 )
Number or Numeral Name String
4
Types of Expressions
Primitive expressions:
Call expressions:
2 add 'hello'
max ( 2 , 3 )
Operator
Number or Numeral Name String
4
Types of Expressions
Primitive expressions:
Call expressions:
2 add 'hello'
max ( 2 , 3 )
Operator Operand Operand
Number or Numeral Name String
4
Types of Expressions
Primitive expressions:
Call expressions:
2 add 'hello'
max ( 2 , 3 )
Operator Operand Operand
max(min(pow(3, 5), -4), min(1, -2))
Number or Numeral Name String
4
Types of Expressions
Primitive expressions:
Call expressions:
2 add 'hello'
max ( 2 , 3 )
Operator Operand Operand
max(min(pow(3, 5), -4), min(1, -2))
Number or Numeral Name String
4
An operand can also be a call expression
Types of Expressions
Primitive expressions:
Call expressions:
2 add 'hello'
max ( 2 , 3 )
Operator Operand Operand
max(min(pow(3, 5), -4), min(1, -2))
Number or Numeral Name String
4
An operand can also be a call expression
Discussion Question 1
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Discussion Question 1
What is the value of the final expression in this sequence?
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Discussion Question 1
What is the value of the final expression in this sequence?
>>> f = min
5
Discussion Question 1
What is the value of the final expression in this sequence?
>>> f = min
>>> f = max
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Discussion Question 1
What is the value of the final expression in this sequence?
>>> f = min
>>> f = max
>>> g, h = min, max
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Discussion Question 1
What is the value of the final expression in this sequence?
>>> f = min
>>> f = max
>>> g, h = min, max
>>> max = g
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Discussion Question 1
What is the value of the final expression in this sequence?
>>> f = min
>>> f = max
>>> g, h = min, max
>>> max = g
>>> max(f(2, g(h(1, 5), 3)), 4)
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Discussion Question 1
What is the value of the final expression in this sequence?
>>> f = min
>>> f = max
>>> g, h = min, max
>>> max = g
>>> max(f(2, g(h(1, 5), 3)), 4)
???
5
Discussion Question 1
What is the value of the final expression in this sequence?
>>> f = min
>>> f = max
>>> g, h = min, max
>>> max = g
>>> max(f(2, g(h(1, 5), 3)), 4)
???
5
Environment Diagrams
Environment Diagrams
Environment diagrams visualize the interpreter’s process.
7Interactive Diagram
Environment Diagrams
Environment diagrams visualize the interpreter’s process.
7Interactive Diagram
Environment Diagrams
Environment diagrams visualize the interpreter’s process.
7Interactive Diagram
Environment Diagrams
Frames (right):Code (left):
Environment diagrams visualize the interpreter’s process.
7Interactive Diagram
Environment Diagrams
Statements and expressions
Frames (right):Code (left):
Environment diagrams visualize the interpreter’s process.
7Interactive Diagram
Environment Diagrams
Import statement
Statements and expressions
Frames (right):Code (left):
Environment diagrams visualize the interpreter’s process.
7Interactive Diagram
Environment Diagrams
Import statement
Statements and expressions
Frames (right):Code (left):
Environment diagrams visualize the interpreter’s process.
7
Assignment statement
Interactive Diagram
Environment Diagrams
Import statement
Statements and expressions
Arrows indicate evaluation order
Frames (right):Code (left):
Environment diagrams visualize the interpreter’s process.
7
Assignment statement
Interactive Diagram
Environment Diagrams
Import statement
Statements and expressions
Arrows indicate evaluation order
Frames (right):Code (left):
Environment diagrams visualize the interpreter’s process.
7
Just executed
Assignment statement
Interactive Diagram
Environment Diagrams
Import statement
Statements and expressions
Arrows indicate evaluation order
Frames (right):Code (left):
Environment diagrams visualize the interpreter’s process.
7
Just executed
Next to execute Assignment statement
Interactive Diagram
Environment Diagrams
Import statement
Each name is bound to a valueStatements and expressions
Arrows indicate evaluation order
Frames (right):Code (left):
Environment diagrams visualize the interpreter’s process.
7
Just executed
Next to execute Assignment statement
Interactive Diagram
Environment Diagrams
Name
Import statement
Each name is bound to a valueStatements and expressions
Arrows indicate evaluation order
Frames (right):Code (left):
Environment diagrams visualize the interpreter’s process.
7
Just executed
Next to execute Assignment statement
Interactive Diagram
Environment Diagrams
Name Value
Import statement
Each name is bound to a valueStatements and expressions
Arrows indicate evaluation order
Frames (right):Code (left):
Environment diagrams visualize the interpreter’s process.
7
Just executed
Next to execute Assignment statement
Interactive Diagram
Environment Diagrams
Name Value
Import statement
Each name is bound to a value
Within a frame, a name cannot be repeated
Statements and expressions
Arrows indicate evaluation order
Frames (right):Code (left):
Environment diagrams visualize the interpreter’s process.
7
Just executed
Next to execute Assignment statement
Interactive Diagram
Environment Diagrams
(Demo)
Name Value
Import statement
Each name is bound to a value
Within a frame, a name cannot be repeated
Statements and expressions
Arrows indicate evaluation order
Frames (right):Code (left):
Environment diagrams visualize the interpreter’s process.
7
Just executed
Next to execute Assignment statement
Interactive Diagram
Assignment Statements
8Interactive Diagram
Assignment Statements
8Interactive Diagram
Assignment Statements
8Interactive Diagram
Assignment Statements
8
Just executed
Interactive Diagram
Assignment Statements
8
Just executed
Next to execute
Interactive Diagram
Assignment Statements
Execution rule for assignment statements:
8
Just executed
Next to execute
Interactive Diagram
Assignment Statements
Execution rule for assignment statements:
1. Evaluate all expressions to the right of = from left to right.
8
Just executed
Next to execute
Interactive Diagram
Assignment Statements
Execution rule for assignment statements:
1. Evaluate all expressions to the right of = from left to right.
2. Bind all names to the left of = to those resulting values in the current frame.
8
Just executed
Next to execute
Interactive Diagram
Assignment Statements
Execution rule for assignment statements:
1. Evaluate all expressions to the right of = from left to right.
2. Bind all names to the left of = to those resulting values in the current frame.
8
Just executed
Just executed
Next to execute
Interactive Diagram
Assignment Statements
Execution rule for assignment statements:
1. Evaluate all expressions to the right of = from left to right.
2. Bind all names to the left of = to those resulting values in the current frame.
8
Just executed
Just executed
Next to execute
Interactive Diagram
Discussion Question 1 Solution
9
(Demo)
Interactive Diagram
Discussion Question 1 Solution
9
(Demo)
Interactive Diagram
Discussion Question 1 Solution
9
(Demo)
Interactive Diagram
Discussion Question 1 Solution
9
(Demo)
Interactive Diagram
Discussion Question 1 Solution
9
func min(...)
(Demo)
Interactive Diagram
Discussion Question 1 Solution
9
func min(...) f(2, g(h(1, 5), 3))
(Demo)
Interactive Diagram
Discussion Question 1 Solution
9
func min(...) f(2, g(h(1, 5), 3))
func max(...) 2
(Demo)
Interactive Diagram
Discussion Question 1 Solution
9
func min(...) f(2, g(h(1, 5), 3))
g(h(1, 5), 3) func max(...) 2
(Demo)
Interactive Diagram
Discussion Question 1 Solution
9
func min(...) f(2, g(h(1, 5), 3))
g(h(1, 5), 3) func max(...) 2
func min(...)
(Demo)
Interactive Diagram
Discussion Question 1 Solution
9
func min(...) f(2, g(h(1, 5), 3))
g(h(1, 5), 3) func max(...) 2
h(1, 5) func min(...)
(Demo)
Interactive Diagram
Discussion Question 1 Solution
9
func min(...) f(2, g(h(1, 5), 3))
g(h(1, 5), 3) func max(...) 2
h(1, 5) func min(...)
5 func max(...) 1
(Demo)
Interactive Diagram
Discussion Question 1 Solution
9
func min(...) f(2, g(h(1, 5), 3))
g(h(1, 5), 3) func max(...) 2
h(1, 5) func min(...) 5
5 func max(...) 1
(Demo)
Interactive Diagram
Discussion Question 1 Solution
9
func min(...) f(2, g(h(1, 5), 3))
g(h(1, 5), 3) func max(...) 2
3 h(1, 5)
func min(...) 5
5 func max(...) 1
(Demo)
Interactive Diagram
Discussion Question 1 Solution
9
func min(...) f(2, g(h(1, 5), 3))
g(h(1, 5), 3) 3 func max(...) 2
3 h(1, 5)
func min(...) 5
5 func max(...) 1
(Demo)
Interactive Diagram
Discussion Question 1 Solution
9
func min(...) f(2, g(h(1, 5), 3))
3
g(h(1, 5), 3) 3 func max(...) 2
3 h(1, 5)
func min(...) 5
5 func max(...) 1
(Demo)
Interactive Diagram
Discussion Question 1 Solution
9
func min(...) 4 f(2, g(h(1, 5), 3))
3
g(h(1, 5), 3) 3 func max(...) 2
3 h(1, 5)
func min(...) 5
5 func max(...) 1
(Demo)
Interactive Diagram
Discussion Question 1 Solution
9
func min(...) 4
3
f(2, g(h(1, 5), 3)) 3
g(h(1, 5), 3) 3 func max(...) 2
3 h(1, 5)
func min(...) 5
5 func max(...) 1
(Demo)
Interactive Diagram
Discussion Question 1 Solution
9
func min(...) 4
3
f(2, g(h(1, 5), 3)) 3
g(h(1, 5), 3) 3 func max(...) 2
3 h(1, 5)
func min(...) 5
5 func max(...) 1 3
(Demo)
Interactive Diagram
Defining Functions
Defining Functions
Assignment is a simple means of abstraction: binds names to values
Function definition is a more powerful means of abstraction: binds names to expressions
11
Defining Functions
Assignment is a simple means of abstraction: binds names to values
Function definition is a more powerful means of abstraction: binds names to expressions
<name>(<formal parameters>):
return <return expression>
>>> def
11
Defining Functions
Assignment is a simple means of abstraction: binds names to values
Function definition is a more powerful means of abstraction: binds names to expressions
<name>(<formal parameters>):
return <return expression>
>>> def
Function signature indicates how many arguments a function takes
11
Defining Functions
Assignment is a simple means of abstraction: binds names to values
Function definition is a more powerful means of abstraction: binds names to expressions
<name>(<formal parameters>):
return <return expression>
>>> def
Function signature indicates how many arguments a function takes
Function body defines the computation performed when the function is applied
11
Defining Functions
Assignment is a simple means of abstraction: binds names to values
Function definition is a more powerful means of abstraction: binds names to expressions
<name>(<formal parameters>):
return <return expression>
>>> def
Execution procedure for def statements:
Function signature indicates how many arguments a function takes
Function body defines the computation performed when the function is applied
11
Defining Functions
Assignment is a simple means of abstraction: binds names to values
Function definition is a more powerful means of abstraction: binds names to expressions
<name>(<formal parameters>):
return <return expression>
>>> def
Execution procedure for def statements:
1. Create a function with signature <name>(<formal parameters>)
Function signature indicates how many arguments a function takes
Function body defines the computation performed when the function is applied
11
Defining Functions
Assignment is a simple means of abstraction: binds names to values
Function definition is a more powerful means of abstraction: binds names to expressions
<name>(<formal parameters>):
return <return expression>
>>> def
Execution procedure for def statements:
1. Create a function with signature <name>(<formal parameters>)
2. Set the body of that function to be everything indented after the first line
Function signature indicates how many arguments a function takes
Function body defines the computation performed when the function is applied
11
Defining Functions
Assignment is a simple means of abstraction: binds names to values
Function definition is a more powerful means of abstraction: binds names to expressions
<name>(<formal parameters>):
return <return expression>
>>> def
Execution procedure for def statements:
1. Create a function with signature <name>(<formal parameters>)
2. Set the body of that function to be everything indented after the first line
3. Bind <name> to that function in the current frame
Function signature indicates how many arguments a function takes
Function body defines the computation performed when the function is applied
11
Calling User-Defined Functions
12Interactive Diagram
Calling User-Defined Functions
Procedure for calling/applying user-defined functions (version 1):
12Interactive Diagram
Calling User-Defined Functions
Procedure for calling/applying user-defined functions (version 1):
1. Add a local frame, forming a new environment
12Interactive Diagram
Calling User-Defined Functions
Procedure for calling/applying user-defined functions (version 1):
1. Add a local frame, forming a new environment2. Bind the function's formal parameters to its arguments in that frame
12Interactive Diagram
Calling User-Defined Functions
Procedure for calling/applying user-defined functions (version 1):
1. Add a local frame, forming a new environment2. Bind the function's formal parameters to its arguments in that frame3. Execute the body of the function in that new environment
12Interactive Diagram
Calling User-Defined Functions
Procedure for calling/applying user-defined functions (version 1):
1. Add a local frame, forming a new environment2. Bind the function's formal parameters to its arguments in that frame3. Execute the body of the function in that new environment
12Interactive Diagram
Calling User-Defined Functions
Procedure for calling/applying user-defined functions (version 1):
1. Add a local frame, forming a new environment2. Bind the function's formal parameters to its arguments in that frame3. Execute the body of the function in that new environment
Built-in function
12Interactive Diagram
Calling User-Defined Functions
Procedure for calling/applying user-defined functions (version 1):
1. Add a local frame, forming a new environment2. Bind the function's formal parameters to its arguments in that frame3. Execute the body of the function in that new environment
Built-in function
User-defined function
12Interactive Diagram
Calling User-Defined Functions
Procedure for calling/applying user-defined functions (version 1):
1. Add a local frame, forming a new environment2. Bind the function's formal parameters to its arguments in that frame3. Execute the body of the function in that new environment
Local frame
Built-in function
User-defined function
12Interactive Diagram
Calling User-Defined Functions
Procedure for calling/applying user-defined functions (version 1):
1. Add a local frame, forming a new environment2. Bind the function's formal parameters to its arguments in that frame3. Execute the body of the function in that new environment
Local frame
Original name of function called
Built-in function
User-defined function
12Interactive Diagram
Calling User-Defined Functions
Procedure for calling/applying user-defined functions (version 1):
1. Add a local frame, forming a new environment2. Bind the function's formal parameters to its arguments in that frame3. Execute the body of the function in that new environment
Local frame
Original name of function called
Formal parameter bound to argument
Built-in function
User-defined function
12Interactive Diagram
Calling User-Defined Functions
Procedure for calling/applying user-defined functions (version 1):
1. Add a local frame, forming a new environment2. Bind the function's formal parameters to its arguments in that frame3. Execute the body of the function in that new environment
Local frame
Original name of function called
Formal parameter bound to argument Return value
(not a binding!)
Built-in function
User-defined function
12Interactive Diagram
Calling User-Defined Functions
13
Procedure for calling/applying user-defined functions (version 1):
1. Add a local frame, forming a new environment 2. Bind the function's formal parameters to its arguments in that frame 3. Execute the body of the function in that new environment
Interactive Diagram
Calling User-Defined Functions
A function’s signature has all the information needed to create a local frame
13
Procedure for calling/applying user-defined functions (version 1):
1. Add a local frame, forming a new environment 2. Bind the function's formal parameters to its arguments in that frame 3. Execute the body of the function in that new environment
Interactive Diagram
Calling User-Defined Functions
A function’s signature has all the information needed to create a local frame
13
Procedure for calling/applying user-defined functions (version 1):
1. Add a local frame, forming a new environment 2. Bind the function's formal parameters to its arguments in that frame 3. Execute the body of the function in that new environment
Interactive Diagram
Calling User-Defined Functions
A function’s signature has all the information needed to create a local frame
13
Procedure for calling/applying user-defined functions (version 1):
1. Add a local frame, forming a new environment 2. Bind the function's formal parameters to its arguments in that frame 3. Execute the body of the function in that new environment
Interactive Diagram
Looking Up Names In Environments
14
Looking Up Names In Environments
Every expression is evaluated in the context of an environment.
14
Looking Up Names In Environments
Every expression is evaluated in the context of an environment.
So far, the current environment is either:
14
Looking Up Names In Environments
Every expression is evaluated in the context of an environment.
So far, the current environment is either:
• The global frame alone, or
14
Looking Up Names In Environments
Every expression is evaluated in the context of an environment.
So far, the current environment is either:
• The global frame alone, or
• A local frame, followed by the global frame.
14
Looking Up Names In Environments
Every expression is evaluated in the context of an environment.
So far, the current environment is either:
• The global frame alone, or
• A local frame, followed by the global frame.
Most important two things I’ll say all day:
14
Looking Up Names In Environments
Every expression is evaluated in the context of an environment.
So far, the current environment is either:
• The global frame alone, or
• A local frame, followed by the global frame.
Most important two things I’ll say all day:
An environment is a sequence of frames.
14
Looking Up Names In Environments
Every expression is evaluated in the context of an environment.
So far, the current environment is either:
• The global frame alone, or
• A local frame, followed by the global frame.
Most important two things I’ll say all day:
An environment is a sequence of frames.
A name evaluates to the value bound to that name in the earliest frame of the current environment in which that name is found.
14
Looking Up Names In Environments
Every expression is evaluated in the context of an environment.
So far, the current environment is either:
• The global frame alone, or
• A local frame, followed by the global frame.
Most important two things I’ll say all day:
An environment is a sequence of frames.
A name evaluates to the value bound to that name in the earliest frame of the current environment in which that name is found.
E.g., to look up some name in the body of the square function:
14
Looking Up Names In Environments
Every expression is evaluated in the context of an environment.
So far, the current environment is either:
• The global frame alone, or
• A local frame, followed by the global frame.
Most important two things I’ll say all day:
An environment is a sequence of frames.
A name evaluates to the value bound to that name in the earliest frame of the current environment in which that name is found.
E.g., to look up some name in the body of the square function:
• Look for that name in the local frame.
14
Looking Up Names In Environments
Every expression is evaluated in the context of an environment.
So far, the current environment is either:
• The global frame alone, or
• A local frame, followed by the global frame.
Most important two things I’ll say all day:
An environment is a sequence of frames.
A name evaluates to the value bound to that name in the earliest frame of the current environment in which that name is found.
E.g., to look up some name in the body of the square function:
• Look for that name in the local frame.
• If not found, look for it in the global frame.(Built-in names like “max” are in the global frame too, but we don’t draw them in environment diagrams.)
14
Looking Up Names In Environments
Every expression is evaluated in the context of an environment.
So far, the current environment is either:
• The global frame alone, or
• A local frame, followed by the global frame.
Most important two things I’ll say all day:
An environment is a sequence of frames.
A name evaluates to the value bound to that name in the earliest frame of the current environment in which that name is found.
E.g., to look up some name in the body of the square function:
• Look for that name in the local frame.
• If not found, look for it in the global frame.(Built-in names like “max” are in the global frame too, but we don’t draw them in environment diagrams.)
(Demo)14
